Gear changing transmissions for motor vehicles are usually controlled or shifted, respectively, by means of an actuating device within hand-reach of the driver. Regularly, the actuating devices, such as shift lever or selector lever, in these cases are applied and positioned between the front seats or on the center console of the motor vehicle, for instance.
The constructive and ergonomic requirements for these actuating devices, for gear changing transmissions, are diverse. For instance, to suggest to the driver a realistic feeling of the transmission operation, for ergonomic reasons, it is required for this genus of the actuating devices that feedback is provided during the activation, optical as well as a clear haptic or tactical, respectively, about the actual shift condition or operating condition, respectively, of the transmission. It is especially desired to obtain, under all possible conditions, a safe handling of the transmission-actuating device without the need to look at the actuating device.
In the case of the earlier commonly used, strictly mechanical transmission actuation, or in the case of a mechanical link between the actuating device and the gear changing transmission—for instance by means of a cable pull or rods—the position of the selector lever or the actuating device, respectively, and the actual transmission setting always matches because of the mechanical link between the actuating device and the transmission. Also, possible actuating locks in the transmission become noticeable, due to the mechanical transfer, when operating the selector lever or the actuating devices.
With the increasingly applied electro-hydraulic or shift-by-wire actuation, respectively, in gear shifting transmissions, a mechanical link does not exist anymore between the actuating device or the selector lever, inside the passenger compartment, and the transmission in the motor compartment. In fact, the transfer of shift commands of the actuating device to the motor vehicle transmission occur, in a “shift-by-wire” transmission, almost exclusively by means of electric or electronic signals, followed by an electro-hydraulic transformation of the shift commands directly to the transmission.
This applies partially to modern gear changing transmissions, but mainly to the current generations of automatic gear boxes which, today, are mostly completely servo-actuated or electro-hydraulic remote controlled, respectively.
Especially in shift-by-wire-actuated gear changing transmissions, and based on the background of the servo-actuated transmission operation, actuating devices are increasingly being applied which only have a comparable short shift travel and which need little actuating force. Hereby, the haptic feedback, meaning the gear shift status feedback to the user, is basically limited to overcoming the locking of the actuating device. In such actuating devices, however, which only require a short shift travel and shift forces, and which just provide minimal haptic feedback with regard to the shift state, operating errors are possible.
For example, in the case of shifting through several transmission steps, not locked in the actual vehicle state, like shifting back and forth between the drive step “D” and “R”, shifting through and beyond the neutral position “N”, it might inadvertently occur that the actuating device is shifted beyond the drive step “R”, whereby the park lock will unintendedly become engaged.
This situation can occur, for instance, when parking or maneuvering at low speed or when swinging the vehicle when stuck in snow. In these cases, often a rapid shifting between the forward gear and reverse gear occurs and attention, at the same time, is focused towards the road. Therefore, the operation of the gear selector device occurs in a haptic mode, not viewing the gear selector device.
In this example and at low speed of the vehicle, in vehicles having a conventional shift scheme layout, the reverse gear and the park lock are not blocked and it can happen that the actual shift moves beyond the drive position “R”. This will cause—at least at low speed—the park lock to engage and, therefore, maneuvering is unintentionally, and by surprise, interrupted.